Perfluorinated aliphatic polyether lubricant with a perfluorinated phenyl compound additive



United States Patent Olice ABSTRACT OF THE DISCLOSURE A lubricantcomprising (1) a major amount of a base fluid of a perfluorinatedaliphatic polyether selected from the group consisting of compoundshaving the following structures:

where n is a positive integer including zero and represents the numberof -CF(X)-CF O units in the mole cule and where X is a member of theclass consisting of fluorine and the perfluoromethyl radical; and

3,393,151 Patented July 16, 1968 By way of illustration of the problemsencountered in the prior art where perfluorinated aliphatic polyetherfluids have been employed as lubricants for mechanical componentscomposed of mild steels, serious corrosion has occurred at temperaturesof from 550 to 600 degrees Fahrenheit; and even the stainless steels andthe hitherto highly regarded titanium alloys have been attacked attemperatures of 600 degrees Fahrenheit. In use with the titanium alloys,moreover, the perfluorinated aliphatic polyether lubricating fluidsthemselves have undergone negative viscosity changes to the detriment ofcontinued lubricating capacity. As temperatures of this order and evenhigher to 700 degrees Fahrenheit and above are encountered withincreasing frequency in highly oxidative or otherwise degradingenvironments, such problems have represented a serious deterrent to theuse of these otherwise desirable lubricating fluids.

It is accordingly an object of this invention to provide improvedlubricants based upon perfluorinated aliphatic polyether neat fluids.

Still another object of the invention is to provide such lubricantswhich will not attack conventional ferrous metals and titanium alloysthereof at elevated temperatures and will not themselves be subject todeleterious change in response thereto.

F3 F3 F3 CF:

wherein n and m are positive integers of at least 2; and (2) aperfluorophenyl phosphorus compound selected from the group consistingof (C F P and (C F PO in an amount of about 0.05 to 5.0 percent byweight of the base fluid.

This application is a continuation-in-part of application Ser. No.475,608, filed July 28, 1965, now abandoned, by the inventors of thepresent application.

The invention described herein may be manufactured and used by or forthe United States Government for governmental purposes without paymentto us of any royalty thereon.

The present invention relates to lubricants composed of perfluorinatedaliphatic polyethers having a perfluoroaryl-type additive admixedtherewith.

In the advancing technology of lubrication, particularly as it has beenmotivated by the sophistication of aerospace exploration and travelencountering ever-increasing speeds and wide ranges in temperatures,myriad new lubricant compositions have been required to replace thetraditional petroleum based oils and greases. Particularly significantimprovements in these areas have been achieved by the use ofperfluorinated aliphatic polyethers.

While these polyethers have, in and of themselves, demonstrated improvedlubricity over a broad range of environmental extremes of temperatureand other degrading influences, their use has been seriously limited bythe interaction between them and the mechanical components with whichthey are used. At temperatures on the order of 500 degrees Fahrenheitand above for example, the perfluorinated aliphatic polyethers have apronounced tendency to attack most metals in such a way that the metalparts become pitted or corroded to the detriment of their properfunctioning. The reverse action of the metals on the fluids on the otherhand is such that they undergo deleterious changes in viscosity andother important properties. While these problems could be successfullyavoided in certain limited applications, for example by metallurgicalrefinements such as forming the parts to be lubricated of metals with ahigh nickel or cobalt content, these expedients would be extremelycostly and diflicult to maintain within reasonable tolerances.

Yet another object of the invention is to provide an improved additivefor perfluorinated aliphatic polyether lubricating fluids.

Still another object of the invention is to render perfluorinatedaliphatic ether lubricating fluids available for use in mechanismswithout the need tor complex and critical metallurgical modifications.

These and other object and advantages which will appear from thefollowing disclosure are achieved by the incorporation with theperfluorinated aliphatic polyether neat fluids of minor proportions byweight of perfluoroaryl-type additives and particularly of thoseperfluoroaryl compounds containing at least one perfluoroaryl group anda Group IV or Group V element of the Mendeleevian Periodic Table ofElements. Although particularly outstanding results have been achievedin the case of phosphorus perfluoroaryl compounds, the correspondingtin, germanium and silicon compounds are useable. While tests haveindicated that the eflectiveness of such additives is significant whenthey are present in weight ratios of as low as 0.05 percent of the totallubricant composition and that they do not impair the performancecapabilities of the lubricant when they are present in a weight ratio ofas high as 5 .0 percent, an additive-to-total composition weight ratiowithin the range of from 0.2 percent to 0.5 percent by weight hasdemonstrated optimum properties. Although the perfluoroaryls are notreadily soluble at room temperatures in the perfluorinated aliphaticpolyethers and the relatively low molecular Weight compounds aresomewhat volatile, it appears that they are nonetheless capable ofinhibiting the corrosion of high-iron-containing steels as Well astitanium alloys to which they are exposed, even at temperatures on theorder of 600 degrees Fahrenheit and in oxidizing atmospheres. Moreover,the use of some of the higher molecular weight analogs of theseperfluoroaryl compounds, and particularly of those containingphosphorus, improves corrosion resistance at elevated temperatures, as aprimary result in all probability, of the decrease in the volatility orsublimation tendencies of the higher molecular weight materials.

More specifically the perfluorinated aliphatic polyethers employed inthe present invention as the base or neat 3 4 fluid are selected fromthe group consisting of polyethers which formulation was bubbled oneliter of air per hour of the following structure: for a specified periodof time at a constant temperature,

namely, 550 F. or 600 F. The 550 F. tests were conducted for 48 hourswhile the 600 F. tests were for 24 hours. The apparatus employed for thetests consisted where n is a positive integer including zero andrepresents of an oxidation test tube and take-off adapter coupled thenumber of -CF(X)CF -O- units in the moleto an air entry tube with themetal specimens to be tested. cule and where X is a member of the classconsisting of An aluminum block bath was the heating means and anfluorine and the perfluoromethyl radical; and overboard test (no refluxcondenser) was used. The re- F3 0 F: C F3 0 F3 wherein n and m arepositive integers of at least 2. sults of this testing procedure aresummarized in Tables The polyethers constituting base fluid B above arepre- 15 IV below.

TABLE 1.NOMINAL COMPOSITION OF METAL SPECIMENS Specimen Percent CPercent Mn Percent P Percent S Percent Cr Percent Mo Percent Si (l) 1000steel 1 .08 max. .25. 40 .040 max. 050 max. (2) 1020 steel 18. 23 30-.60 040 max. 050 max. (3) 1040 steel .37. 44 .60. 00 .040 max. 050 max.(4) 4130 steel 28-. 33 40-. G0 040 max. 040 max. (5) 4140 steel 1 .38.43 75-1. 00 040 max. .040 max. (5) 410 stainless steel max. 1.00 max.1.00 max. (7) 52100 bearing steel 1 .95-1. 1O 45 .025 max. .025 max.

Percent 0 Percent Cr Percent V Percent W Percent Mo (8) M-1 tool steel 12 .80 4.00 1.00 1. 50 8. 50 (9) M-2 tool steel 1 2 .85 4.00 2.00 6.255.00

Percent Al Percent V Percent Mn Percent N Percent 0 Percent H Percent FePercent O (10) Titanium, 0 111-4 V alloy W491i) 5. 5%). 75 3. 5-4. 5 .07max. 10 max. 015 max. 40 max. max. (11) Titanium, 4 A14 Mn lloy -4925)3. 0-5. 0 3. 0-5. 0 07 max. .15 max. 50 max.

l AISI-American Iron and Steel Institute. Reference for Specimens 6 and8-11: Metals Handbook, Vol. 1. Prop- SAESociety of Automotive Engineers.cities and Selection of Metals," 8th ed., American Society for Metals,

3 AMS-Aeronautical Material Specifications Metals Park, Ohio, 1961.

Reference for Specimens 1-5 and 7: AsME Handbook, Metals Propertics, 1sted., Mc Grew, Hill, New York 1954.

pared by the Polymerization of a Perfillomolefin epoxide, TABLE2.COMPATIBILITY OF POLYMERIC PERFLUORI- such as hexafluoropropyleneepoxide and tetrafiuoroethyl- NATED ALIPHATIC POLYETHER FORMULATIONSWITH ene epoxide, by hydrolysis of the resulting polymerization 410STAINLESS STEEL (SS) product and the simultaneous fluorination anddecarboxyl- [Fluid A] ation of the h drol zed roduct. A more detaileddescrip- Corrosion Efiect, weight tion of the ma irmer in wliich thepolyethers of base fluid B Addltwe Fund A g*g gg3,$g,{ of 410 areprepared is set forth in US. Patent No. 3,242,218. Similarly a completedescription of the manner in which wt Percent +0.01 the polyethersconstituting the base fluid A are prepared is given in US. Patent No.3,214,478 as amended by the +002 Certificate of Correction, appendedthereto, dated 5 July 19 None +0.49

The eifectiveness of the perfluorinated aliphatic polyether base fluidsA and B above plus a perfiuoroaryl-type 5 [Fluid B] additive, such as aperfluorinated phenyl compound, for Corrosion Effect, weight reducingand inhibiting corrosion in certain steels and Addmvem FluldB gg gg ggg"r410 titanium alloys is well illustrated by the following oxidationtests. In each instance the specimen of steel or alloy wtp t P 0.00 wasimmersed in a formulation consisting of (1) either None 56 base fiuld Aor B and about perceilt by Welght of a Summary 01 Oxidation-CorrosionTest Conditions 600 F., 20 m1. perfiuoroaryl-type addltlVe 511611 38triperfluorophenyh sample, one liter/hr. air rate, 24-hour duration,overboard, one metal phosphine and triperfluorophenylphosphine oxidethrough speclmen' TABLE 3.COMPATIBILITY OF POLYMERIC PERFLUORINATEDALIPHATIC POLYETHER FORMULATIONS WITH 1006, 1020, 1040, 4130 AND 4140STEELS [Fluid A] Test Test Corrosion ElIect, weight change (mg/cm?) ofsteel Additive in Fluid A temp. duration specimens F.) (hrs) 0.25 wt.percent P 550 48 +0.04 +0.32 +0.05 +0.02 +0.02

None 550 48 +0. 19 +0.55 +0. 40 +0.45 +0.27

1.0 Wt. percent P 000 24 0. 02 +0. 04 +0. 22 -0. 17 +0. 37

0.5 wt. percent PO (500 24 +0.09 +0. 12 +0. 12 +0. 30 +0. 06

None 000 24 +0. 63 +0. 24 +0. 98 +1. 00 +2. 18

See footnote at end of table.

TABLE 3-Continued [Fluid B] Test Test Corrosion Eflect, wei ht chan e mcm. of steel Additive in Fluid B t(enI1 p). dlblifitlljul sfaecimens g l0.5 wt percent P 600 24 +0. 07 21 +0.05 +0. 07 +0. 10

0.5 wt. percent (@PO 600 24 0. 08 0. 01 +0. 03 +0. 03 0.

None 600 24 +0. 21 +0. 37 +1. 62 +1. 00 +2. 44

Summary of Oxidation-Corrosion Test Conditions: ml. sample,one-liter/hr. air rate, overboard, 5 metal specimens.

TABLE 4.COMPATIBILITY OF POLYMERIC PERFLUORI- NATED ALIPHATIC POLYE'IHERFORMULATIONS WITH M-l AND M-Z TOOL STEELS AND 52100 BEARING STEELSummary of Oxidation-Corrosion Test Conditions 600" F., 20 ml. sample,one-liter/hr. air rate, 24-hour duration, overboard, three specimens.

From the above test data it will be apparent that there was only nominalor no evidence of corrosion on those specimens in which the neat or basefluid A or B contained the perfluoroaryl phosphorus compounds as anadditive. On the other hand the specimens immersed in the neat fluid Aor B without any additive were significantly corroded.

While the within invention has been described above in connection withcertain specific embodiments and examples thereof, it is to beunderstood that the foregoing particularization has been for the purposeof illustration only and does not limit the scope of the invention as itis more precisely defined in the subjoined claims.

We claim:

1. A lubricant comprising 1) a major amount of a base fluid of aperfluorinated aliphatic polyether selected from the group consisting ofcompounds having the following structures:

where n is a positive integer including zero and repre- TABLE5.COMPATIBILITY OF POLYMERIC PERFLUO RINATED ALIPHATIC POLYETHERFORMULATIONS WITH TITANIUM ALLOYS [Fluid A] Kinematic Fluid lossviscosity Corrosion Efiect, weight change Additive in Fluid A (percent)el113(r)1 g% at (mg/em!) of titanium alloys (percent) 4% A14% Mn 0% Al4%v 0.05 wt. percent P 1. 8 -3. 5 +0.07 +0. 00

0.5 wt. percent P 1. 0 +1.0 +0. 07 +0. 00

0.5 wt. percent P0 0. 5 0 +0. 00 +0.00

None 7. 1 14. 7 0. 35 +0. 17

[Fluid B] Kinematic Fluid loss viscosity Corrosion Effect, weight changeAdditive in Fluid B (percent) clligrgg at (mg/cm?) oi titanium alloys(percent) 4% 104% Mn 6% Al4% v 0.5 wt. percent (@P 0.8 +1.8 +0. 00 +0.04

5.0 wt. percent P 0.2 +0.03 +0.02

None 17. 8 36. 7 -0. -0. 13

*Not measured due to insoiubility of 5.0 wt. percent P in Fluid B at F.

Summary of Oxidation-Corrosion Test Conditions: 600 F., 20 ml. sample,one-liter/hr. air rate, 24-hour duration, overboard, two metalspecimens.

molecule and where X is a member of the class consisting of fluorine andthe perfluoromethyl radical; and

CFa CFa CFa CFz 4. The lubricant of claim 1 in which the polyether basefluid has the following structure:

where n is a positive integer including zero and represents the numberof CF(X)CFO units in the molecule and where X is a member of the classconsisting of fluorine and the perfluoromethyl radical.

wherein n and m are positive integers of at least 2.

5. The lubricant of claim 1 in which the phosphorus compound is (C F P.

6. The lubricant of claim 1 in which the phosphorus compound is (C F PO.

7. The lubricant of claim 3 in which the phosphorus compound is (C F P.

8. The lubricant of claim 4 in which the phosphorus compound is (C F PO.

9. The lubricant of claim 7 in which the phosphorus compound is presentin the amount of about 0.2 to 0.5 percent by weight of the base fluid.

10. The lubricant of claim 8 in which the phosphorus compound is presentin the amount of about 0.2 to 0.5 percent by weight of the base fluid.

References Cited UNITED STATES PATENTS 5/1959 Wilson 252--49.9 XR 4/1966Stark 252--46.4

